This application claims the priority of German Application No. 10 2004 037 116.4 filed Jul. 30, 2004, the disclosure of which is expressly incorporated by reference herein.
This invention relates to a hydraulic linear drive, of a hydraulic transmission actuator. Preferred embodiments of the invention relate to a hydraulic linear drive for a transmission actuator comprising a piston/cylinder unit in which an adjusting piston is arranged in a cylinder housing so that the piston is longitudinally displaceable and divides a cylinder housing space into at least two pressure spaces, hydraulic lines communicating hydraulic oil through hydraulic lines leading to the pressure spaces, and a sealing element arranged on one of the adjusting piston and the cylinder housing for mutually sealing the two pressure spaces with respect to one another.
Hydraulic linear drives are used, for example, in automatic transmissions for synchronizing the gears (see, for example, Johannes Loomann, Zahnradgetriebe [Toothed Gears], 2nd edition, pages 156 ff.).
With the generic hydraulic linear drives, the double piston bordered by two pressure spaces is displaced to the left or right by a pressure acting accordingly, with the two pressure spaces being sealed in many applications by sealing elements provided on the outer circumference of the piston.
In hydraulic transmission actuators in particular, high adjusting forces are applied in synchronization of the gear wheels, requiring reliable and permanent sealing and/or separation of the two pressure spaces.
An object of the present invention is therefore to improve upon the sealing of the two pressure spaces in the area of the piston/cylinder unit. This object is achieved according to certain preferred embodiments of the invention by providing a linear drive for a transmission actuator comprising a piston/cylinder unit in which an adjusting piston is arranged in a cylinder housing so that the piston is longitudinally displaceable and divides a cylinder housing space into at least two pressure spaces, hydraulic lines communicating hydraulic oil through hydraulic lines leading to the pressure spaces, and a sealing element arranged on one of the adjusting piston and the cylinder housing for mutually sealing the two pressure spaces with respect to one another, wherein the sealing element is a sealing ring accommodated in a ring groove on the cylinder housing and sealed on its inside with respect to the adjusting piston and which can be acted upon by hydraulic oil on its outside.
Due to a pressure acting on the sealing ring accommodated in a peripheral groove in the cylinder housing, a sealing force is additionally exerted on it, ensuring a reliable sealing of the two pressure spaces separated by the adjusting piston.
Additional advantageous embodiments and refinements of the hydraulic linear drive are possible through the features described herein and in the claims.
A particularly effective seal is obtained according to certain embodiments of the invention when the sealing ring has a groove with a V-shaped cross section on its outside, while the cross section on the inside tapers in the direction of the adjusting piston. The contact pressure of the sealing ring against the adjusting piston is thus increased due to the linear pressure thereby generated.
For the sealing ring to be acted upon by hydraulic oil during the adjustment of the piston, the pressure difference between the two pressure spaces is picked up in an advantageous manner and sent via a pressure balance to the sealing ring on its outside according to certain preferred embodiments of the invention.
As an alternative to the permanent hydraulic oil feed described above, with the help of a switching valve, the pressure supply to the sealing ring may be designed to be controllable. The advantage of an additional hydraulic seal that can be activated and deactivated any number of times is that when using the hydraulic linear drive as a hydraulic transmission actuator, for example, the sealing ring is acted upon by hydraulic oil only during the synchronization phase during which higher adjusting forces must be applied.
Two exemplary embodiments of this invention are depicted in the drawing and are described in greater detail below.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.